6 Sir  william  Hamilton’s  Account  of. \ See. 
enquiry  I found,  that  a confiderable  trade  of  this  ma- 
terial is  carried  on  between  this  town  and  Holland,  where 
they  grind  down  this  fort  of  ftone  by  wind-mills  into  a 
powder,  which  they  ufe  as  a puzzolane  for  all  their  build- 
ings under  water.  This  alfo  correfponds  with  an  idea 
mentioned  in  one  of  my  former  letters  to  the  Royal  So- 
* 
ciety,  that  the  tuffas  of  Naples  were  compofed  of  a puz- 
zolane, prepared  by  volcanic  fire  deep  in  the  bowels  of 
the  earth,  and,  mixing  with  water  at  the  time  of  its  ex- 
plofion,  formed  a fort  of  natural  mortar  or  cement.  The 
Dutch  reduce  it  again  to  its  priftine  ftate  of  puzzolane. 
I flatter  myfelf  you  will  excufe  my  fending  you  fuch 
crude  and  hafty  remarks,  as  my  time  will  not  allow  me 
to  examine  further  : I only  mean  to  point  out  this  cu- 
rious country  for  further  inveftigation.  What  I have 
juft  feen  confirms  me  in  the  opinion,  that  volcanic  opera- 
tions are  much  greater  agents  of  nature  than  is  generally 
imagined. 
I am,  See. 
